Shopify now has support for the payment gateway Braintree.

From the Braintree homepage:

Braintree Financial is a leading provider of electronic payment services such as credit cards, electronic checks. The company is a single source provider offering customers a one stop for all of their payment processing needs. Braintree offers cutting edge technology, high touch consulting services to better manage costs and streamline operations, and other value added services such as financing and security compliance.

Special thanks to Michael J. Mangino who contributed the code to to ActiveMerchant.